Study on accumulated crystallization characteristics of amorphous Ge2Sb2Te5 induced by multi-pulsed laser irradiations with different fluences. (5th June 2018)

• Record Type: Journal Article
• Authors: Fan, T; Liu, F R; Li, W Q; Guo, J C; Wang, Y H; Sun, N X; Liu, F
• Is Part Of: Semiconductor science and technology. Volume 33:Number 7(2018:Jul.)
• Publication Date: 2018-06-05
• Subjects: Ge2Sb2Te5 -- accumulated crystallization -- multi-pulsed laser -- laser fluences; Semiconductors -- Periodicals; 621.38152
• DOI: 10.1088/1361-6641/aac370
• Languages: English
• ISSNs: 0268-1242

Abstract

Abstract: Accumulated crystallization characteristics of amorphous Ge2 Sb2 Te5 (a-GST) films induced by multi-pulsed laser irradiations with different fluences were investigated by x-ray diffraction (XRD), Raman spectroscopy and spectrophotometer. Solid-state transformation was performed at low fluence (LF, 30.5 mJ cm −2 ), whereas melting-cooling transformation dominated at medium and high fluence (MF, 45.7 and HF, 61 mJ cm −2 ). Solid-state transformation induced by subsequent LF pulses promoted the growth and coalescence of grains, linearly increasing the average grain size, accordingly causing blue-shifts of the Raman spectral peaks. For MF/HF pulse irradiated films, the relatively high laser fluence increased the melting depth and reduced the volume fraction of the crystalline state induced by individual pulses, thereby increasing the threshold of laser pulse numbers for XRD detectable crystallization. However, the remelting depth induced by subsequent MF/HF laser pulse progressively decreased. The remelting-recrystallization process refined grain sizes, which improved the red-shifts of Raman spectral peaks. Moreover, optical contrast increased dramatically compared to single laser irradiation and five-level storage could be realized for a linear increase of optical contrast. The present study is fundamental for realizing the potential of multi-level devices.